1. Field of the Invention
This invention relates to a method for preparing polycyclic aromatic hydrocarbons. More particularly, the invention relates to an improved method for preparing polycyclic aromatic hydrocarbons from an aromatic hydrocarbon and two molecules of styrene in good yield.
2. Description of Prior Art
The distyrenated aromatic hydrocarbon, that is, one of polycyclic aromatic hydrocarbons, is prepared by aralkylating an aromatic hydrocarbon molecule with two molecules of styrene. The distyrenated aromatic hydrocarbon is quite excellent in compatibility and thermal stability, and the compound itself is effectively used as a plasticizer, a lubricant, an electrical insulating oil and so forth. In addition, by hydrogenerating the distyrenated aromatic hydrocarbon, it is employed as a high-energy fuel and a lubricating oil. Therefore, the distyrenated aromatic hydrocarbon is one of the important industrial raw materials.
In connection with the method for preparing the distyrenated aromatic hydrocarbons by aralkylating aromatic hydrocarbons with styrenes, there have been proposed several methods in, for example, British Pat. No. 896,864, No. 959,355 and No. 977,322, in which methods, alkylbenzenes are aralkylated with styrenes by using concentrated sulfuric acid or a solid acid such as acid clay. In all of these conventional methods, both the monostyrenated product and the distyrenated product are simultaneously formed, and therefore, these methods are not serviceable for the preparation of the sole distyrenated product.